Similar to the case of substances other than easily polymerizable substances, distribution of liquids such as the transfer of liquid or feeding of liquid is carried out in the production processes of easily polymerizable substances such as (meth)acrylic acid, (meth)acrylate esters and (meth)acrolein.
“Easily polymerizable substances” polymerize extremely easily and polymers form easily during their production and distribution or other forms of handling. Therefore, polymerization inhibitors are added to easily polymerizable substances so that they can be handled while inhibiting their polymerization. If a polymerization inhibitor is added to an easily polymerizable substance, polymerization is inhibited even if it is allowed to remain for a fixed period of time in a pipe or other form of line used for its distribution. Pipes and so forth used for distribution of liquids containing easily polymerizable substances are designed and produced on the basis of this premise.
In order to ensure smooth distribution of liquid containing easily polymerizable substances, it is preferable that the easily polymerizable substance flows through a pipe or other type of line within a predicted retention time.
A flow control valve or flow meter is provided at an intermediate location in a line used for distribution of a liquid containing an easily polymerizable substance in order to ensure smooth operation of a production device and so forth. This flow control valve or flow meter may malfunction during the course of use. Consequently, the flow of liquid containing an easily polymerizable substance must be temporarily interrupted during repair or replacement of the flow control valve or flow meter. Therefore, a shutoff valve is typically provided in a line upstream or downstream from the flow meter or flow control valve in order to stop the flow of liquid containing an easily polymerizable substance.
When repairing or replacing the flow control valve or flow meter, the flow control valve or flow meter is repaired or replaced after closing a shutoff valve provided upstream or downstream there from to temporarily interrupt the flow of liquid containing an easily polymerizable substance.
In addition, in the case of having a considerable effect on the operation of a production device and so forth when the flow of the liquid containing an easily polymerizable substance is interrupted, a method is typically employed in which a bypass line is provided for the flow control valve or flow meter, and a shutoff valve is provided in this bypass line.
FIG. 1 is a schematic block drawing showing an example of a line through which flows a liquid containing an easily polymerizable substance. In addition, FIG. 2 is a schematic block drawing showing another example of a line through which flows a liquid containing an easily polymerizable substance.
In the lines shown in FIGS. 1 and 2, during the time flow control valve 2 or flow meter 3 provided in line 1 is operating normally, liquid containing an easily polymerizable substance flows by opening upstream shutoff valve 4 and downstream shutoff valve 5, and closing bypass shutoff valve 7 provided in bypass line 6.
The reason for allowing the liquid containing an easily polymerizable substance to flow by closing bypass shutoff valve 7 in this manner is because the entire amount of the liquid containing an easily polymerizable substance is allowed to flow through flow control valve 2 or flow meter 3, the flow rate is accurately controlled in flow control valve 2, and the flow rate is accurately indicated in flow meter 3.
In this type of line, in the case flow control valve 2 or flow meter 3 has malfunctioned, first bypass shutoff valve 7 is opened to ensure a flow of liquid containing an easily polymerizable substance to a degree that does not have a considerable effect on the operation of a production device and so forth. Next, upstream shutoff valve 4 and downstream shutoff valve 5 are closed to interrupt the flow of the easily polymerizable substance through line 1 and allow repair or replacement of flow control valve 2 or flow meter 3.
However, if bypass shutoff valve 7 is completely closed while liquid containing an easily polymerizable substance is flowing through line 1, the liquid containing an easily polymerizable substance remaining in bypass line 6 can no longer be renewed, and as a result, the liquid containing an easily polymerizable substance ends up remaining in bypass line 6 beyond the predicted retention time. If an easily polymerizable substance remains in bypass line 6 for a long period of time, it polymerizes and forms a polymer resulting in this polymer clogging bypass line 6. When bypass line 6 becomes clogged, bypass line 6 cannot be used when repairing or replacing flow control valve 2 or flow meter 3, thereby forcing operation of the production device and so forth to be temporarily interrupted and having a considerable effect on the factory overall.